Refractive index sensor based on a silica microsphere whispering gallery mode resonator

We investigated the excitation of whispering gallery modes (WGMs) in a silica microsphere by evanescent field coupling method using a ~2 micrometer diameter fiber taper. Based on this configuration we have developed a sensitive refractometric sensor and observed a red-shift of the WGM resonances with the increase of the surrounding medium refractive index. A sensitivity of ~114 nanometer per RIU has been achieved in the range of refractive indices from 1.3963 to 1.4004.